Get id value from same table in query

I have this table setup:

 id, order_nr

id, orders_id,ref_backorder

Some data:

id order_nr
1  012345
2  0123456

id, orders_id, ref_backorder
1   2          1
1   1           

the ref_backorder is a reference to another row in the same table.

Expected output:
    id, ref_backorder
    1    012345
    2    null

My query:

SELECT, o.ref_backorder`
FROM orders_cart o 
LEFT JOIN orders ON o.ref_backorder` = 

How can i get the ref_backorder as order_nr? ref_backorder is an id from a row. In this case row 1, in row 1 we have an orders_id 2. The value of orders_id 2 (0123456) is the value what I want to show in the query.

Can you join the table to itself?


Seems the query could be this

select o.order_nr
from order 
inner join orders_cart as c on c.ref_backorder =
where c.orders_id = 2

SELECT, A.orders_id, A.ref_backorder, B.order_nr FROM orders_cart AS A
JOIN orders AS B ON
    A.orders_id =

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